Bumble Bees of the Susa Valley (Hymenoptera Apidae)

Bulletin of Insectology 63 (1): 137-152, 2010 ISSN 1721-8861 Bumble bees of the Susa Valley (Hymenoptera Apidae) Aulo MANINO, Augusto PATETTA, Giulia BOGLIETTI, Marco PORPORATO Di.Va.P.R.A. - Entomologia e Zoologia applicate all’Ambiente “Carlo Vidano”, Università di Torino, Grugliasco, Italy Abstract A survey of bumble bees (Bombus Latreille) of the Susa Valley was conducted at 124 locations between 340 and 3,130 m a.s.l. representative of the whole territory, which lies within the Cottian Central Alps, the Northern Cottian Alps, and the South-eastern Graian Alps. Altogether 1,102 specimens were collected and determined (180 queens, 227 males, and 695 workers) belonging to 30 species - two of which are represented by two subspecies - which account for 70% of those known in Italy, demonstrating the particular value of the area examined with regard to environmental quality and biodiversity. Bombus soroeensis (F.), Bombus me- somelas Gerstaecker, Bombus ruderarius (Mueller), Bombus monticola Smith, Bombus pratorum (L.), Bombus lucorum (L.), Bombus terrestris (L.), and Bombus lapidarius (L.) can be considered predominant, each one representing more than 5% of the collected specimens, 12 species are rather common (1-5% of specimens) and the remaining nine rare (less than 1%). A list of collected specimens with collection localities and dates is provided. To illustrate more clearly the altitudinal distribution of the different species, the capture locations were grouped by altitude. 83.5% of the samples is also provided with data on the plant on which they were collected, comprising a total of 52 plant genera within 20 plant families. The eight predominant Bombus species point out remarkable differences in botanical choices, in fact only three genera (Epilobium, Onobrychis, and Trifolium) were visited by all eight species, and showed very different frequencies between the species. Key words: altitude, Bombus, flora visited, mountain species, western Alps. Introduction these studies show however unequivocally that 5 of the 43 species recorded in Italy have not been found lately The genus Bombus sensu lato Latreille 1802 (Hymenop- anymore. tera Apidae), comprising about 240 species present in In Italy, although there are bumble bee subspecies most continents, is distributed mainly in areas of typical of the South and the islands, the number of taxa Europe, Asia and North America with a cold and tem- present in the North is higher because of the species perate climate (Williams, 1998; Benton, 2006). The with a boreal-alpine distribution and of those living in bumble bees are the only social insect whose distribu- the mountains at medium and/or high altitudes, that can tion extends up to the Arctic regions, where bumblebees thus be defined as “orophilous”. The distribution of are characterized by active nest temperature control and such species is clearly affected by the altitude, as al- increased pilosity that make them well adapted to the ready proved by Pittioni (1938) and confirmed by the cold (Pouvreau, 1984). very rich literature afterwards; a recent review of this As regards the altitudinal range, bumble bees are pre- matter is given by the papers by Iserbyt et al. (2008) and sent from sea level up to 4,250 m a.s.l., varying consid- Iserbyt (2009), and the references they quote. In Pied- erably in size and density of the pubescence. However, mont (North-western Italy), this phenomenon was high- although the species of high altitudes are generally more lighted for the "Waldensian Valleys" of the Cottian hairy, it is not clear if there is a correlation between Alps, on the basis of collections made between 1946 hairiness and altitude (Pouvreau, 1984). and 1970, by Comba (1960 and 1972) and Comba and Bumble bees are an important component of ecosys- Comba (2001). tems and their pollinating activity is essential for the The wide variability of geo-morphological and cli- conservation of many plant species. Really because their matic conditions of the Alps, and their level of anthro- presence depends on the abundance and diversity of pogenic disturbance, suggested extending the observa- flora, they are useful indicators of environmental health tions to a contiguous area. This was done by choosing (Macdonald, 2003). In the global decline in biodiversity, the Susa Valley for its extensive and complex hydro- bees are not the exception, unfortunately. The decline, graphic network, the significant elevation difference be- triggered by habitat fragmentation and loss of useful tween the valley and the highest peaks, the large exten- flora, is now documented in Europe especially for social sions of alpine meadows and the ease of access also to bee species (Williams, 1986; Westrich, 1989; Banaszak, high elevations. Moreover, the bumble bee fauna on the 1995; Biesmeijer et al., 2006; Fitzpatrick et al., 2007; morainic hills at the valley outlet in the high Piedmon- Kosior et al., 2007; Williams et al., 2007). tese plain had been recently investigated (Quaranta et Information available on the Italian bumble bee fauna al., 2004). is less than that relative to other countries; therefore it is The territory is located in the Central Cottian Alps, in difficult to point out changes in the distribution and in the Northern Cottian Alps, and the South-eastern Graian the abundance of bumble bees in Italy. Records up to Alps (Marazzi, 2005). On the basis of the geomor- 1995 were assembled by Intoppa et al. (1995) and were phological evolution, it can be divided into three seg- recently reviewed along with later research (Intoppa et ments: High Susa Valley upstream of Oulx, Middle al., 2009), but further investigations are much needed; Susa Valley between Oulx and Susa, and Lower Susa Valley, between Susa and the valley outlet. In the main summer, consistent with the climatic conditions and the valley, which has a curved course with an approxi- growth of the flora, in 114 sites representative of the mately east-west direction, the river Dora Riparia flows, whole territory (figure 1); 94 sites were visited only into which, leaving out the smaller hydrographic net- once, the others twice or more (table 1). On the occasion work, three secondary branches flow: the Dora di Bar- of each visit to each site, bumble bees showing different donecchia, fueled in its initial part by the streams com- colour patterns (Intoppa, 2000) were sampled; whenever ing from Vallée Etroite and Valle di Rochemolles; the possible some specimens of each colour pattern were Dora di Cesana, formed by the streams Ripa and collected. Thuras, and the stream Cenischia. The river basin, cov- In the course of investigations conducted in Susa Val- ering an area of 1,261 km2, extends from 3,538 m a.s.l. ley over the years 1973, 1976-'77, 1984-'85 and 1993, of the Rocciamelone - also placed in an eccentric posi- 89 specimens of bumble bees had been collected in 12 tion with respect to the course of the river - to 300 m sites. They were kept in the collection of Di.Va.P.R.A. a.s.l. of the valley outlet. The highest peaks, on which and the relative data were added and processed together the dorsal watershed separating the valley from the ad- with the 2001-2006 data to obtain a more complete spe- jacent basins is articulated, often include relief exceed- cies list for the valley. They are presented here even ing 3,000 m a.s.l.. though some were previously included in the catalogue by Intoppa et al. (1995): i.e. three records of 1973, relat- ing to the municipality of Rubiana, and other specimens, Materials and methods collected in the years 1984-'85, reported with the generic location “Valle di Susa”. The area in which the study was conducted includes the For each bumble bee, capture date and location were entire valley of the Dora Riparia, which is currently di- recorded; the latter was georeferenced to determine alti- vided into the mountain communities of Alta Valle di tude and UTM WGS84 co-ordinates. Where possible, Susa and Bassa Valle di Susa and Val Cenischia and the plant on which the bumble bee was foraging was politically in some territories belonging to France (basin collected and determined by reference to Aeschimann et of Mont Cenis, Col de Mongenèvre and Vallée Etroite). al. (2004). Some small areas, which are located along the water- The classification up to the generic level was made re- shed between the valley of the Dora Riparia and that of ferring to Michener (2000); for the subdivision into the Chisone, but included in the catchment area of the subgenera the simplified classification proposed by Wil- latter, have also been taken into account in the munici- liams et al. (2008) was followed, while for the identifi- pal districts of Usseaux and Pragelato. cation of species and subspecies and the relative no- Observations and collections were made from 2001 to menclature the work by Intoppa et al. (2009) was 2006 during visits that have taken place in spring and adopted. Figure 1. Collection sites. Localities are numbered according to table 1; shaded areas are part of the French territory. 138 Table 1. Collection sites, subdivided by municipal district (Italy) and mountain territory (France), with their altitude, UMT WGS 84 co-ordinates (East-North) 32N time zone, and the indication of the year(s) they were visited (number of visits in brackets). Locality Site m a.s.l. UTM WGS 84 year (visits) ITALY 1984 (8) 1.1 Avigliana Drubiaglio 340 375810 4994860 1985 (11) 2.1 Bardonecchia Lago Patarè 2810 329800 4999300 2003 (1) 2.2 Lago Sommeiller 2980 330230 4999870 2003

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